At the present time proportional navigation is used to guide most tactical missiles to high speed maneuvering air targets. This technique has also been used against much slower surface targets, although in this latter case there are two good reasons for using pursuit guidance instead.
First, implementation of pursuit guidance using a velocity-vane or weathercock stablized seeker is very simple: certainly much simpler than any known implementation of proportional navigation. Second, in the presence of gravity pursuit guidance yields a straighter flight path to the target.
The velocity-vane implementation of pursuit guidance has been available a number of years in commercial guidance equipment sold by and marketed throughout the world by the Texas Instrument Company. This "Weathercock or Velocity-vane Seeker System" has been sold to as many as 50 countries and comprises generally speaking a statically stable seeker head on the front of a rotary pivoted member called a boom. The weathercock or velocity-vane contains a four-quadrant laser detector. By means of a laser beam scattered from the target the Texas Instrument weathercock seeker system would in effect guide a missile or bomb onto a stationary target on a still or windless day. It is well known in the art however that against a moving surface target, or in the presence of a crosswind, pursuit guidance as implemented by the weathercock system developed by the Texas Instrument Co. has fundamental limitations. Specfically, the bomb or missile will always miss the designated target under these conditions by distances typically as high as forty (40) feet.